For use in transmission power control, control of a transmission mode such as adaptive modulation, and demodulation processing in a receiver, a digital radio communication apparatus typically includes a means for measuring communication line quality such as the SNR (Signal to Noise power Ratio).
As a conventional communication-line-quality estimating technology, for example, a technology regarding OFDM (Orthogonal Frequency Division Multiplexing) is disclosed in Patent Literature 1 described below. Patent Literature 1 describes that known signals are mapped onto subcarriers and an OFDM receiver receives the known signals transmitted between a transmitter and the receiver. Then in the receiver, after modulation components of the known signals are removed, the value of the difference in power between adjacent known signals is established as a noise power estimation value. Subsequently, the estimated noise power estimation value is subtracted from the total reception signal power so as to obtain a desired signal power estimation value. Finally, the ratio of the desired signal power estimation value and the noise power estimation value is calculated to establish the estimated SNR.